Charged particle beam apparatuses have many functions, in a plurality of industrial fields, including, but not limited to, inspection of semiconductor devices during manufacturing, exposure systems for lithography, detecting devices and testing systems. Thus, there is a high demand for structuring and inspecting specimens within the micrometer and nanometer scale.
Charged particle beam devices are typically operated under vacuum conditions. Still, molecules of the residual gas, possibly also molecules desorbed from surfaces of the charged particle beam device, e.g. from extractor, anode, apertures and the like, can adsorb on the emission surface of an emitter. This adsorption of molecules can cause fluctuations of the emission current.
To counteract the adsorption, or even deposition, of particles on the emitter, the emitter can be subjected to flash cleaning. Flash cleaning is typically done by shortly heating the emitter to a high temperature, e.g. 2000 K, such that the adsorbed molecules are desorbed and the emitter is purged. Flash cleaning can be repeated periodically as needed.
However, after flash cleaning, it is found that the emission current may still be different from what it was before. The variations can e.g. consist in drift and/or fluctuation, in particular when flash cleaning is repeated from time to time. While flash cleaning eliminates or reduces the destabilization of the emission current due to adsorption of residual gas molecules, other sources of destabilization are introduced.
Thus, to avoid this undesired effect, there is a need for an improved method for operating a charged particle device, in particular a method for stabilizing the emission current, and for a corresponding device.